Typas Athanasios, Hengge Regine
Institut für Biologie, Mikrobiologie, Freie Universität Berlin, Königin-Luise-Str. 12-16, 14195 Berlin, Germany.
Mol Microbiol. 2006 Feb;59(3):1037-51. doi: 10.1111/j.1365-2958.2005.04998.x.
In vitro, the sigma(s) subunit of RNA polymerase (RNAP), RpoS, recognizes nearly identical -35 and -10 promoter consensus sequences as the vegetative sigma70. In vivo, promoter selectivity of RNAP holoenzyme containing either sigma(s) (Esigma(s)) or sigma70 (Esigma70) seems to be achieved by the differential ability of the two holoenzymes to tolerate deviations from the promoter consensus sequence. In this study, we suggest that many natural sigma(s)-dependent promoters possess a -35 element, a feature that has been considered as not conserved among sigma(s)-dependent promoters. These -35 hexamers are mostly non-optimally spaced from the -10 region, but nevertheless functional. A +/- 2 bp deviation from the optimal spacer length of 17 bp or the complete absence of a -35 consensus sequence decreases overall promoter activity, but at the same time favours Esigma(s) in its competition with Esigma70 for promoter recognition. On the other hand, the reduction of promoter activity due to shifting of the -35 element can be counterbalanced by an activity-stimulating feature such as A/T-richness of the spacer region without compromising Esigma(s) selectivity. Based on mutational analysis of sigma(s), we suggest a role of regions 2.5 and 4 of sigma(s) in sensing sub-optimally located -35 elements.
在体外，RNA聚合酶（RNAP）的σ亚基RpoS识别与营养型σ70几乎相同的-35和-10启动子共有序列。在体内，含有σ（Esigma(s)）或σ70（Esigma70）的RNAP全酶的启动子选择性似乎是通过两种全酶耐受启动子共有序列偏差的不同能力来实现的。在本研究中，我们表明许多天然的依赖σ的启动子具有-35元件，这一特征在依赖σ的启动子中一直被认为是不保守的。这些-35六聚体与-10区域的间距大多并非最佳，但仍具有功能。与17 bp的最佳间隔长度有+/- 2 bp的偏差或完全不存在-35共有序列会降低启动子的整体活性，但同时在与Esigma70竞争启动子识别时有利于Esigma(s)。另一方面，由于-35元件移位导致的启动子活性降低可以通过间隔区富含A/T等活性刺激特征来抵消，而不会损害Esigma(s)的选择性。基于对σ的突变分析，我们认为σ的2.5区和4区在感知位置欠佳的-35元件中发挥作用。
